For encoding of video data, the H.264 video encoding method, which is an ITU-T (International Telecommunication Union-Telecommunications Standards Section) recommended international standard, for example, is used. A technology based on the H.264 video encoding method is described in the following Non-patent Document 1, for example.
In the above-mentioned H.264 video encoding method, redundancy of video frames is decreased and information volume is decreased by compensating motion and encoding motion vectors. According to this method, a region of which one motion vector can compensate is decreased, so as to support subtle motion and increase prediction accuracy of inter-frame prediction. On the other hand, since the number of motion vectors increases and information volume becomes enormous, this increase must be suppressed. As a method for increasing prediction accuracy while decreasing the number of motion vectors, a method disclosed in the following Patent Document 1 has been proposed.    Patent Document 1: Japanese Patent Application Laid-Open No. H2-62180    Non-patent Document 1: Kakuno et al, “H.264/AVC Textbook Impress Standard Textbook Series”, Impress Net Business Company, 2004